Filters are used in a wide variety of applications where it is desired to separate particles or other substances from a fluid stream (e.g., a stream of gas). Applications of filters include removing substances from flue gases such as those from coal and oil fired power generation plants. Such flue gases may contain substantial varieties and quantities of environmental pollutants, such as sulfur oxides (SO2 and SO3), nitrogen oxides (NO and NO2), mercury (Hg) vapor, and particulate matters (PM). In the United States, burning coal alone generates about 27 million tons of SO2 and 45 tons of Hg each year.
The destructive effects of various pollutants on human health and on the ecosystem have long been recognized. For example, SOx and NOx have been linked to the outbreak of respiratory diseases in affected areas. They may also form acid rain, which damages forests, fisheries, and architectures. As for Hg, it is a potent toxin to the nervous system. Exposure to mercury can affect the brain, spinal cord, and other vital organs.
Environmental regulations require significant reductions in mercury emissions. These regulations extend to different industries; presenting challenges in various types of facilities (e.g., coal-fired power generation plants).